Process for the production of a reducing gas for blast furnace

ABSTRACT

THIS INVENTION RELATES TO A PROCESS FOR THE PRODUCTION OF A REDUCING GAS FOR USE IN A BLAST FURNACE SAID PROCESS COMPRISING SEPARATELY PREHEATING A HYDROGEN FUEL AND SEPARATELY PREHEATING THE SUPPORTOR OF COMBUSTION TO BE USED IN THE PARTIAL COMBUSTION FURNACE WHERE THE REDUCING GAS IS PRODUCED TO A TEMPERATURE IN THE RANGE OF 800*-1500* C; FEEDING THE PREHEATED SUPPORTER OF COMBUSTION TO THE PARTIAL COMBUSTION FURNACE TOGETHER WITH THE FUEL WHICH HAS BEEN PREHEATED TO AT LEAST 600* C, COOLING IF NECESSARY THE OBTAINED GASES TO A TEMPRATURE SUITABLE FOR INTRODUCTION INTO THE BLAST FURNACE AND; FEEDING THE GASES TO THE BLAST FURNACE.

May 28, 1974 ca. PAGANl 3,313,229

PROCESS FOR THE PRUDUCTION OF A REDUCING GAS FOR BLAST FURNACE Filed Sept. 3, 1971 3 Sheets-Sheet 1 INVENTOR.

B I MW.W

ATTORNEY May 28, 1974 G. PAGANI 3,813,229

PROCESS FOR THE PRODUCTION OF A REDUCING GAS FOR BLAST FURNACE Filed Sept. 5, 1971 3 Sheets-Sheet 2 v v 1e A V is 3 E3 1 6 I HT? FIG. 2

ATTORNEY May 28, 1974 G. PAGANI 3,313,229

PROCESS FOR THE PRODUCTION OF A REDUCING GAS F OR BLAST FURNACE Filed Sept. 5, 1971 s sheets-Shoat 5 FIG. 5

plNVENT OR.

ATTORNEY United States Patent 3,813,229 PROCESS FOR THE PRODUCTION OF A REDUCING GAS FOR BLAST FURNACE Giorgio Pagani, Milan, Italy, assignor to Snam Progetti, S.p.A., San Donato Milanese, Italy Filed Sept. 3, 1971, Ser. No. 177,630 Claims priority, application Italy, Sept. 3, 1970, 29,300/70 Int. Cl. C01b 2/14 US. Cl. 48-196 R 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for the production of a reducing gas for use in a blast furnace said process comprising separately preheating a hydrocarbon fuel and separately preheating the supporter of combustion to be used in the partial combustion furnace where the reducing gas is produced to a temperature in the range of 800-l500 C.; feeding the preheated supporter of combustion to the partial combustion furnace together with the fuel which has been preheated to at least 600 C.; cooling, if necessary, the obtained gases to a temperature suitable for introduction into the blast furnace and; feeding the gases to the blast furnace.

The present invention relates to a process for the production of a reducing gas for blast furnaces.

More particularly, the present invention relates to an extremely advantageous process for the production of a reducing gas which can be used in blast furnaces, said process making it possible to obtain a gas of very high quality from the metallurgical point of view.

A very important requirement in the metallurgical field is that of reducing as much as possible the coke consumption in the blast furnace.

The reason for this requirement lies in the increasing cost of the metallurgical coke and in the difliculty of finding pit-coal having the characteristics desired for the production of metallurgical coke.

In a conventional coke blast furnace, the heat necessary for the heat balance is obtained by oxidizing a part of the coke to CO with air (highly exothermic reaction), while the reduction of the iron oxides is effected both directly by the coke in the high temperature zone (highly endothermic reaction) and by the CO produced in the medium temperature zone (slightly exothermic reaction). It is obvious that having set the preheating of the burning air, the amounts of air and coke necessary for the thermal balance of the blast furnace are defined.

If we want to reduce the coke consumption, we can operate only in one way, namely, eliminating completely or nearly the direct reduction by coke, providing for the lack of reducing gas by introduction of another reducing gas (produced outside the blast furnace) to the bottom of the shaft, i.e. to a zone having a temperature of about 1000 C. and wherein the processes of reduction with C0 of the iron oxides are carried out.

The basic characteristics which a reducing gas to be used in a blast furnace must have, are described hereinafter.

It is required that the temperature be of about 900- 1000 C. and that the content of CO +H O be as low as possible, the degree of exploitation of the reducing gas being connected just to the H 0 and C0 content of the same.

As a suggestion we consider excellent as gas having a content of CO +H O=3% by volume, while a reducing gas having a content of CO +H O=1O% by volume is very near the limit which is not convenient for use for reduction in a blast furnace.

3,813,229 Patented May 28, 1974 It is known, in fact, that the products obtained by reduction of an iron oxide by means of hydrogen and carbon monoxide are, besides iron, H 0 and C0 The reduction reactions are equilibrium reactions and therefore, as such, are negatively affected by the presence in the gaseous phase of H 0 and CO at high partial pressures.

In the case of high concentrations in the reducing gas of said two compounds, the degree of exploitation of the same gas is low in the sense that, for some values of the partial pressure of the two gases in the gaseous mixture, the whole mass of the reducing gas passes unchanged through the blast furnace.

At the throat of said blast furnace there are, therevfore, in the case of a low degree of utilization, large amounts of unreacted H and CO which cannot be easily used.

The production of a reducing gas, starting for instance from methane as raw material, can be effected essentially according to the following process:

steam reforming partial combustion cycle thermal cracking Among said processes only the first two succeeded.

The steam reforming process is the process, at present, more economical for the production of hydrogen starting from CH or a light gasoline.

Nevertheless the necessity of having a reducing gas at a temperature of about 1000 C. with a reduced content of CO and H 0, makes as known, the production cycle complex and difiicult.

The process of partial combustion with oxygen is particularly suitable for the gasification of heavy liquid fuels.

The working temperature is generally comprised in the range of from 1200" C. to 1400" C. and the produced gas may be introduced, after a slight cooling, directly into the blast furnace, even if its not negligible H 0 and CO content lowers its yield.

Drawbacks of said process, besides the not good composition of the produced gas, is the oxygen consumption, which remarkably affects the cost of the reducing gas.

The oxidation reaction, for instance, of methane to CO is slightly exothermic but the developed heat is not willcient to bring the combustion products to the desired temperature, which will be reached only by burning a part of the methane to CO and H 0.

The high preheating of the reactants allows the reducing of the part of CH, which is completely burnt.

A content of CO +H O equal to about 7% or higher is obtained, however.

Said H O+CO content is due, as said, to the necessity of bringing the products of the partial combustion to the desired temperature; furthermore it is due to the loss of heat and to the possible endothermic cracking reactions of the fuel with production of carbon black; all this involves an increase of the amount of fuel which must be completely burnt and therefore an increase of H O+CO content in the reducing gas.

For the processes of partial combustion with oxygen it is to be noted that the fact that the necessity of operating at high temperatures involves necessarily such concentrations that the degree of exploitation of said gases in the blast furnace process is lowered.

Said concentration can be remarkably reduced when the preheating of the fuel and of the supporter of combustion is brought to such levels that the amount of fuel completely burnt is lowered.

For the fuel preheating there are upper stability limits which is the case of methane is 600 C Also for the supporter of combustion, in case oxygen is used, for reasons of resistance of the metals to the oxidation, there are limits not higher than 400 C.500 C.

There has now been found, and this is a feature of the present invention, a partial combustion process which makes it possible to produce a reducing gas having excellent metallurgical characteristics without necessarily requiring the use of oxygen.

It is an object of the present invention to provide a process for the production of a reducing gas for blast furnace, which process consists of a conventional process of partial oxidation of hydrocarbons (as for example methane, virgin naphtha fuel oil and the like) allowing use, as supporter of combustion, air or possibly air enriched with oxygen, and also making it possible to obtain, with the particular preheating medium and/ or the preheating level of the supporter of combustion, a reducing gas for blast furnace of very high quality, having a total content of CO +H O, referred to the hydrogen and carbon monoxide present in the gas, lower than 5% by volume and in any case considerably lower than the one obtainable by the conventional process of partial combustion with oxygen and therefore presenting a high utilization degree in the blast furnace.

In the process according to the present invention, use is preferably made of the technique of preheating of the burning air typical of the blast furnaces (in the blast furnaces air is preheated to 1200 C.-1300 C. or to higher temperatures in Cowper regenerators) for preheating the supporter of combustion, preferably air, up to temperatures close to the ones of the partial combustion furnace.

By operating in said way the H O+CO content in the produced reducing gas is lowered to very low values, even if the burning medium is air.

Obviously other preheating systems may be used, the level of the preheating temperatures reached in the process according to the present invention being always the same.

In this respect it is to be noted that the preheating to temperatures close to the ones of the combustion furnace allowed by the particular preheating system of the present invention or by another system, involves and con temporaneously allows the use of air, since the presence of the inert N does not influence, or influences marginally, the thermal balance of the reactor and therefore the CO +H O content, thus avoiding the drawbacks connected with the use of oxygen.

According to the present invention, surprisingly, it is possible to succeed in eliminating two very big drawbacks of the process of partial combustion for the production of gas to be introduced into the blast furnace, i.e. the excessive content of CO +H O in the reducing gas and the oxygen consumption, therefore making the process extremely competitive with respect to known processes.

When, for flooding reasons, the amount of gases introduced into the blast furnace has to be reduced, we will operate, in the process according to the present invention, with enriched air rather than with air alone, as aforesaid. In the process according to the present invention, the air necessary for the production of the reducing gas is generally preheated to temperatures ranging from 800 C. to 1500 C. (preferably from 1200 C. to 1400 C.) in conventional Cowper regenerators well known in the metallurgical art.

Said preheating may be effected in the same Cowper regenerators used for preheating the air sent to the bottom of the blast furnace, deriving then the burning air, possibly enriched with O necessary for the partial combustion; or Cowper regenerators different from the ones of the blast furnace may be provided, said last regenerators working obviously always in the same well known manner.

The air preheated and possibly enriched with oxygen is fed to the partial combustion reactor together with the fuel equally preheated within the limits and with known methods.

In order to reduce as much as possible the formation of CO +H O it is preferable that the preheating temperature of the burning air be higher than or equal to that of the partial combustion reactor, the previously established operative range being always the same.

On leaving the reactor, the reducing gas, which may contain carbon black, is generally at a temperature higher than the one it must have at the introduction into the blast furnace (about 1000 C.); therefore said gas must be cooled. The cooling may be effected by making the gas pass within the boiler producing steam or, according to the process of the present invention, by a quench with coke-oven gas, hydrogen rich and easily available in a steel plant, or by quench with CH, which, during cracking, absorbs heat and produces hydrogen and carbon black, both of which are used in the blast furnace.

Also by working with a coke-oven gas a part of the CH contained therein cracks obtaining H and carbon black, both of which are used in the blast furnace. However other cooling methods may be used.

The so cooled reducing gas is introduced into the blast furnace.

An interesting possible realization of the process according to the present invention is the one wherein the pre-heating of the burning air is effected as already described with the difference that the partial combustion is effected not in an apparatus separate from the blast furnace but in a series of tuyeres, or more properly of burners, placed inside the blast furnace at its bottom; in this last case, the temperature regulation of the reducing gases may be effected, if necessary, by a convenient injection into the blast furnace of a cool gas, for example coke-oven gas.

We will now give three illustrative, but unrestrictive, examples of realization of the process according to the present invention, referring always to the case wherein some Cowper regenerators are used for preheating the air introduced into the blast furnace and furthermore the Cowper regenerators used for preheating the air introduced into the blast furnace are also used for preheating the burning air to be fed to the partial combustion furnace.

With reference to FIG. 1 of the drawings, the air or the air enriched with oxygen enters the working Cowper regenerator 2 through 1, while the other Cowper regenerator 3 is in regeneration (both the working Cowper regenerator and the one in regeneration may be more than one or, as already said, two distinct Cowper batteries may be provided, the one for preheating the air to be fed directly into the blast furnace and the other one for preheating the burning air to be fed to the partial combustion).

The air flowing through 4, preheated to temperatures close to the ones of the partial combustion, is divided in two streams: the one which enters the blast furnace directly through 5, the air mainfold 6 and the duct 7; the other one which enters the partial combustion furnace 9 through 8 whereto also the already preheated fuel is fed through 10.

The produced reducing gas leaves the furnace 9 through 11, is cooled in 12 and enters the bottom of shaft 16 through 13, 14 and 15.

From the bottom of the blast furnace, through 17, the produced cast iron is discharged while the throat gas is discharged from the top through 18.

In FIG. 2, apparatus is shown wherein the burners 21, directly inserted in the blast furnace, are used.

In said figure 20 represents the fuel manifold.

In FIG. 3, apparatus is shown wherein the gases leaving the partial combustion furnace 9 are cooled by quench with a gas fed through 19, said gas being for instance a coke-oven gas.

Two numerical examples of the process according to the present invention will now be given with reference to FIGS. 1 and 3 without limiting in any case the invention to them.

The indicated values refer to the production of 1000 kg. of cast iron.

EXAMPLE 1 Percent H 37.89 CO 19.42 CH 0.20 N 40.62 CO 0.31 H 0 1.56

This gas was passed through the boiler 12 wherein it was cooled down to 1000 C. and then it was introduced into the blast furnace.

EXAMPLE 2 With reference to FIG. 3, 1278 Nm. of air were flowed through the regenerator 2 and its temperature rose from 40 C. to 1250" C.

Through 5, 600 Nm. were fed directly to the blast furnace; the remaining 678 Nm. were fed, through 8, to the partial combustion furnace 9 into which, through 10, 261 Nm. of CH preheated at 600 C. were introduced.

From the exit of furnace 9, 1315 Nm. of gases at 1200 C. were obtained, said gases having the compositions shown in Example 1; to said gases, through 19, 185 Nm. of gases having a temperature of 25 C. were added and the following composition by volume:

Percent H 56.95 00 4.75 co 3.80 CH 23.80 N; 5.70 H 0 5.00

In this way 1520 Nm. of gas at 1000 C. having the following composition by volume were obtained:

the carbon black content being of 7.75 grams per Nm. of gas.

Said gas was fed to the blast furnace.

What is claimed is:

1. A process for the production of a reducing gas for a blast furnace having a combined H 0 and CO content of less than 5% which comprises separately preheating methane to a temperature of 600 C. and separately preheating air to a temperature in the range of 800-1500 C., feeding the preheated air and the methane to a partial combustion furnace and thereafter passing said reducing gas for a blast furnace to a blast furnace.

2. A process for the production of a reducing gas for a blast furnace having a combined H 0 and CO content of less than 5% which comprises separately preheating a hydrocarbon fuel to a temperature of at least 600 C., and separately preheating a supporter for combustion selected from the group consisting of air and air enriched with oxygen to a temperature in the range of 800-1500 C., feeding the preheated supporter of combustion and the hydrocarbon fuel to a partial combustion furnace and thereafter passing said reducing gas for a blast furnace to a blast furnace.

3. Process for the production of a reducing gas for a blast furnace as claimed in claim 2 characterized in that the supporter of combustion used in the partial combus tion furnace is air.

4. Process for the production of a reducing gas for a blast furnace as claimed in claim 2 characterized in that the hydrocarbon fuel in the partial combustion furnace is selected from the group consisting of CH virgin naphtha and fuel oil.

5. Process for the production of a reducing gas for a blast furnace as claimed in claim 2 characterized in that the air that is fed to the partial combustion furnace is preheated to a temperature in the range from 1200 C. to 1400 C.

6. Process for the production of a reducing gas for a blast furnace as claimed in claim 2 characterized in that the gases leaving the partial combustion furnace are cooled by making said reducing gas for a blast furnace flow through a boiler for the production of steam prior to passing said reducing gas for a blast furnace to a blast furnace.

7. Process for the production of a reducing gas for a blast furnace as claimed in claim 2 characterized in that the gases leaving the partial combustion furnace are cooled by injection in the gaseous mass of a hydrogen rich gas prior to passing said reducing gas for a blast furnace to a blast furnace.

References Cited UNITED STATES PATENTS 2,537,708 1/ 1951 Scharmann 48215 X 3,250,601 5/1966 Jenny 48l96 R 3,591,364- 7/1971 Reynolds et a1. 42 3,536,455 10/1970 Bogdany et al. 252-373 3,013,876 12/1961 Jenny 48196 R X 2,591,700 4/1952 Jacolev et al. 48l96 R 3,694,373 9/1972 Schlingcr ct al 252373 JOSEPH SCOVRO'NEK, Primary Examiner US. Cl. X.R. 

